fix: don't override log level from state for standalone agents (#8784) (#8858)

* fix: don't override log level from state for standalone agents

* doc: add changelog fragment

* fix: add unit test for NewAgentInfoWithLog

* fix: derive unprivileged from utils.HasRoot

(cherry picked from commit e8f759b)

Co-authored-by: Panos Koutsovasilis <[email protected]>

Author: mergify[bot]

changelog/fragments/1751455886-correct-log-level-for-standalone-agents.yaml

@@ -0,0 +1,5 @@
+kind: bug-fix
+summary: Ensure standalone Elastic Agent uses log level from configuration instead of persisted state
+component: elastic-agent
+pr: https://github.com/elastic/elastic-agent/pull/8784
+issue: https://github.com/elastic/elastic-agent/issues/8137

internal/pkg/agent/application/info/agent_info.go

@@ -60,14 +60,17 @@ type AgentInfo struct {
 	esHeaders map[string]string
 }
 
+// for unit testing
+var doLoadAgentInfoWithBackoff = loadAgentInfoWithBackoff
+
 // NewAgentInfoWithLog creates a new agent information.
 // In case when agent ID was already created it returns,
 // this created ID otherwise it generates
 // new unique identifier for agent.
 // If agent config file does not exist it gets created.
 // Initiates log level to predefined value.
 func NewAgentInfoWithLog(ctx context.Context, level string, createAgentID bool) (*AgentInfo, error) {
-	agentInfo, isStandalone, err := loadAgentInfoWithBackoff(ctx, false, level, createAgentID)
+	agentInfo, isStandalone, err := doLoadAgentInfoWithBackoff(ctx, false, level, createAgentID)
 	if err != nil {
 		return nil, err
 	}
@@ -76,9 +79,13 @@ func NewAgentInfoWithLog(ctx context.Context, level string, createAgentID bool)
 		return nil, fmt.Errorf("failed to determine root/Administrator: %w", err)
 	}
 
+	if !isStandalone {
+		level = agentInfo.LogLevel
+	}
+
 	return &AgentInfo{
 		agentID:      agentInfo.ID,
-		logLevel:     agentInfo.LogLevel,
+		logLevel:     level,
 		unprivileged: !isRoot,
 		esHeaders:    agentInfo.Headers,
 		isStandalone: isStandalone,

internal/pkg/agent/application/info/agent_info_test.go

@@ -0,0 +1,80 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License 2.0;
+// you may not use this file except in compliance with the Elastic License 2.0.
+
+package info
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/elastic/elastic-agent/pkg/utils"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewAgentInfoWithLog(t *testing.T) {
+	hasRoot, err := utils.HasRoot()
+	require.NoError(t, err, "failed to check for root")
+
+	for _, tc := range []struct {
+		name                string
+		levelFromConfig     string
+		isStandalone        bool
+		persistentAgentInfo *persistentAgentInfo
+		expected            *AgentInfo
+	}{
+		{
+			name:            "standalone agent",
+			levelFromConfig: "debug",
+			isStandalone:    true,
+			persistentAgentInfo: &persistentAgentInfo{
+				ID:             "testID",
+				Headers:        nil,
+				LogLevel:       "info",
+				MonitoringHTTP: nil,
+			},
+			expected: &AgentInfo{
+				agentID:      "testID",
+				logLevel:     "debug",
+				unprivileged: !hasRoot,
+				esHeaders:    nil,
+				isStandalone: true,
+			},
+		},
+		{
+			name:            "fleet managed agent",
+			levelFromConfig: "debug",
+			isStandalone:    false,
+			persistentAgentInfo: &persistentAgentInfo{
+				ID:             "testID",
+				Headers:        nil,
+				LogLevel:       "info",
+				MonitoringHTTP: nil,
+			},
+			expected: &AgentInfo{
+				agentID:      "testID",
+				logLevel:     "info",
+				unprivileged: !hasRoot,
+				esHeaders:    nil,
+				isStandalone: false,
+			},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			prevDoLoadAgentInfoWithBackoff := doLoadAgentInfoWithBackoff
+			defer func() {
+				doLoadAgentInfoWithBackoff = prevDoLoadAgentInfoWithBackoff
+			}()
+			doLoadAgentInfoWithBackoff = func(ctx context.Context, forceUpdate bool, logLevel string, createAgentID bool) (*persistentAgentInfo, bool, error) {
+				return tc.persistentAgentInfo, tc.isStandalone, nil
+			}
+
+			ai, err := NewAgentInfoWithLog(context.Background(), tc.levelFromConfig, true)
+			assert.NoError(t, err, "could not create agent info")
+			assert.Equal(t, tc.expected, ai, "agent info does not match")
+		})
+	}
+}